I can confirm that the USB-C power port is not for power only. In SSH, the lsusb command shows a USB 3.0 5000M root hub.
Also, @dragon788 states in the thread:
"The most awesome and unexpected feature of the BrumeW has been the USB-C port also appears as an Ethernet connection if you happen to have it plugged into a computer or other device capable of supplying enough power for the router to operate. I wasn’t expecting this and it blew my mind because it means that I should be able to far more easily route only certain traffic from my computer over the “wired” connection while still remaining connected to a work or other wireless connection rather than having to flip back and forth between a work connection and a personal/VPN protected connection.
I’ve tested this on both a Macbook Pro and a Chromebook, and on the Chromebook I was actually just using a USB 3.0 port and not a USB-C/PD port. ChromeOS happily recognized the router as an Ethernet connection once the router had fully booted."
I tried this by plugging the plugging the router’s USB-C port into my PC’s USB-C PD port. Windows 10 detected the router as a RNDIS/Ethernet Gadget and I had to manually install a RNDIS driver. I could then access the Internet over “ethernet” through the router.
It still remains unknown why the router’s USB-C port does not work with a powered hub that has other devices.